643 research outputs found
Coherent states, Path integral, and Semiclassical approximation
Using the generalized coherent states we argue that the path integral
formulae for and (in the discrete series) are WKB exact,if
the starting point is expressed as the trace of with
being given by a linear combination of generators. In our case,WKB
approximation is achieved by taking a large ``spin'' limit: . The result is obtained directly by knowing that the each coefficient
vanishes under the () expansion and is examined by another
method to be legitimated. We also point out that the discretized form of path
integral is indispensable, in other words, the continuum path integral
expression leads us to a wrong result. Therefore a great care must be taken
when some geometrical action would be adopted, even if it is so beautiful, as
the starting ingredient of path integral.Comment: latex 33 pages and 2 figures(uuencoded postscript file),
KYUSHU-HET-19 We have corrected the proof of the WKB-exactness in the section
The Architecture of Discretion: Implications of the Structure of Sanctions for Racial Disparities, Severity, and Net Widening
About four million people are serving a term of probation, parole, or post-release supervision in the United States. Due to the extensive use of incarceration as a punishment for conditions violations, these community supervision programs are a major factor contributing to mass incarceration and, as this Article shows, can play a significant role in exacerbating racial disparities in the criminal legal system.
In recent years, jurisdictions throughout the United States have made reforms to their community supervision programs. A major trend in community supervision reform is the integration of new sanctioning structures, such as âswift and certainâ sanctions, for conditions violations. These changes not only introduce new types of sanctions but also redesign the architecture of the sanctioning process and provide a valuable opportunity to study how the contours of discretion affect bias, severity, and frequency in the imposition of sanctions.
In this Article, I study a statewide probation reform that implemented swift and certain sanctions. I present new empirical evidence on the impact of two key elements of the structure of discretion: the disaggregation of discretion into multiple decision points and the allocation of discretion among various actors in the decision-making process. In addition, this Article includes the first in-depth empirical analysis of swift and certain sanctions on racial disparities.
Using a detailed administrative dataset covering nearly 90,000 probation cases, I find that the introduction of swift and certain sanctioning reforms is associated with a statistically significant increase in the overall rate of incarceration among probationers and a statistically significant decrease in racial disparities in incarceration.
The overall increase in incarceration is driven by the imposition of new jail and prison sanctions introduced by the swift and certain reforms. The decrease in racial disparities appears to be driven by the narrowing of racial disparities associated with probation revocations. These results suggest that disaggregating and reallocating points of discretion may reduce racial disparities but can come at the expense of widening the carceral net
Final-state read-out of exciton qubits by observing resonantly excited photoluminescence in quantum dots
We report on a new approach to detect excitonic qubits in semiconductor
quantum dots by observing spontaneous emissions from the relevant qubit level.
The ground state of excitons is resonantly excited by picosecond optical
pulses. Emissions from the same state are temporally resolved with picosecond
time resolution. To capture weak emissions, we greatly suppress the elastic
scattering of excitation beams, by applying obliquely incident geometry to the
micro photoluminescence set-up. Rabi oscillations of the ground-state excitons
appear to be involved in the dependence of emission intensity on excitation
amplitude.Comment: 4 pages, 4 figures, to appear in Appl. Phys. Let
Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots
We report strong heavy hole-light mixing in GaAs quantum dots grown by
droplet epitaxy. Using the neutral and charged exciton emission as a monitor we
observe the direct consequence of quantum dot symmetry reduction in this strain
free system. By fitting the polar diagram of the emission with simple
analytical expressions obtained from kp theory we are able to extract
the mixing that arises from the heavy-light hole coupling due to the
geometrical asymmetry of the quantum dot.Comment: 4 pages, 2 figure
Current noise of a quantum dot p-i-n junction in a photonic crystal
The shot-noise spectrum of a quantum dot p-i-n junction embedded inside a
three-dimensional photonic crystal is investigated. Radiative decay properties
of quantum dot excitons can be obtained from the observation of the current
noise. The characteristic of the photonic band gap is revealed in the current
noise with discontinuous behavior. Applications of such a device in
entanglement generation and emission of single photons are pointed out, and may
be achieved with current technologies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (2005
Bunching visibility for correlated photons from single GaAs quantum dots
We study photon bunching phenomena associated with biexciton-exciton cascade
in single GaAs self-assembled quantum dots. Experiments carried out with a
pulsed excitation source show that significant bunching is only detectable at
very low excitation, where the typical intensity of photon streams is less than
the half of their saturation value. Our findings are qualitatively understood
with a model which accounts for Poissonian statistics in the number of
excitons, predicting the height of a bunching peak being determined by the
inverse of probability of finding more than one exciton.Comment: 6 pages, 6 figs to appear in Phys. Rev.
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